One of the most basic requirements for any lubricating oil is the proper viscosity for the purpose intended. Automobiles operating in moderate climates normally employ crankcase oils with a viscosity of from 9.6 to 12.9 centistokes at 210.degree. F. (98.9.degree. C.). Such oils are commonly designated SAE 30 in accordance with the viscosity classification system established by the Society of Automotive Engineers. The designation SAE 20 defines a less viscous oil, with a viscosity of between 5.7 and 9.6 centistokes at 210.degree. F. Many turbine lubricants have similar viscosity requirements, 5 to 7 centistokes at 210.degree. F. being a representative range.
Most automobile crankcase oils are formulated from petroleum base oils derived from crude oil by distillation, extraction and other conventional refining techniques. One such oil, a solvent treated neutral oil called 300 Neutral and supplied by the Union Oil Corporation, has a kinematic viscosity of about 8 centistokes at 210.degree. F. and about 70 centistokes at 100.degree. F. (37.8.degree. C.). Its viscosity index is 88. Such an oil can be blended with other oils and suitable additives to produce either an SAE 20 or 30 motor oil or turbine lubricant, as is well known to workers skilled in the art of lubricating oil compounding.
One drawback of petroleum base oils such as the aforementioned 300 Neutral is their tendency to solidify at low temperatures. Thus, 300 Neutral has a pour point of 10.degree. F. (-12.degree. C.). The problem, of course, is the presence in the oil of waxy paraffinic constituents with relatively high melting points. These waxes can be removed to some extent by various "de-waxing" processes. Instead of removing the wax, as an alternative, additives called pour point depressants can be added to the formulation to lower the solidification point. But increasing interest is also being shown in the use of wax-free synthetic base oils -- that is, oils prepared by chemical reaction rather than crude oil refining -- in place of the petroleum base stocks. Two classes of synthetic hydrocarbon are receiving considerable attention, in the area of crankcase oils and turbine lubricants. The first class consists of the linear alpha-olefin oligomers, such as the trimers, tetramers, and higher polymers of n-decene-1, CH.sub.3 -- (CH.sub.2).sub.7 CH=CH.sub.2. These may be prepared by reacting the olefin with conventional polymerization catalysts, such as anhydrous aluminum chloride, organic peroxides, boron trifluoride with promoters such as water, alcohols, or carboxylic acids, and "Ziegler-type" systems such as alkylaluminum halides in combination with titanium halides. Processes for preparing oligomer oils are disclosed by many workers, including Pratt U.S. Pat. No. 3,842,134, Montgomery et al U.S. Pat. No. 2,559,984, Hamilton et al U.S. Pat. No. 3,149,178, Brennan U.S. Pat. No. 3,769,363, and Smith et al U.S. Pat. No. 3,682,823. The second class consists of the dialkylbenzenes, such as di-dodecylbenzene, (C.sub.12 H.sub.25).sub.2 C.sub.6 H.sub.4. These may be prepared by the Friedel-Crafts reaction, wherein benzene is reacted with an olefin or alkyl halide containing the appropriate number of carbon atoms in the presence of a catalyst such as anhydrous aluminum chloride or boron trifluoride. Pappas, U.S. Pat. No. 3,173,965, Bray et al U.S. Pat. No. 3,544,472, Becraft et al U.S. Pat. No. 3,288,716, and others have disclosed processes for the manufacture of dialkylbenzenes. Both the oligomer oils and the dialkylbenzenes offer significant advantages over a conventional petroleum base oil such as 300 Neutral; namely, low pour points, usually -60.degree. F. (-51.1.degree. C.), or below, high viscosity indices (usually 100-110 for dialkylbenzenes, 120-140 for the oligomer oils), and (frequently) better oxidation stability.
Inasmuch as many of the substances capable of polymerizing linear alpha-olefins to form oligomer oils are also catalysts for the addition of olefins to benzene, previous workers have attempted to combine the two reactions and react olefins with benzene in such a way as to effect both polymerization and benzene alkylation. Boux de Casson et al U.S. Pat. No. 2,518,529 describe the simultaneous alkylation and polymerization of a cracked distillate-benzene mixture in the presence of anhydrous aluminum chloride. A representative product of their process had the following properties: a kinematic viscosity of 25.6 centistokes at 100.degree. F. and 4.6 centistokes at 210.degree. F. (calculated from the reported viscosity index of 103); a pour point of -30.degree. C. (-22.degree. F.); an iodine number of 4. Antonsen and Hirschler, U.S. Pat. No. 3,104,267, disclose the polymerization of a linear alpha-olefin in the presence of benzene, using a mixture of titanium tetrachloride and ethyl aluminum dichloride. When polymerization was complete, dry hydrogen chloride or bromide was introduced, thereby causing alkylation of the benzene by the oligomer mixture formed in the first step. A representative product had a viscosity of 48.14 centistokes at 100.degree. F., a viscosity of 6.89 centistokes at 210.degree. F. (calculated from the reported viscosity index of 108), a bromine number of 0.5, and a pour point of +20.degree. F. which is undesirably high. Both these references suggest the desirability of obtaining a product with a minimum of residual unsaturation -- that is, an oil wherein the double bonds of the starting olefin and polyolefins formed therefrom have substantially been eliminated by reaction with the benzene, and the final bromine or iodine number is low.
On the other hand, Romine U.S. Pat. No. 3,812,036 discloses a combination polymerization-alkylation process wherein he seeks to avoid the complete elimination of olefinic products. Romine reacts benzene with a linear alpha-olefin in the presence of an aluminum chloride-nitromethane mixture to obtain an oil preferably comprising between 20 to 50% alkylated benzene compounds and from 50 to 80% olefin oligomers. These products have viscosities in the range of 5 to 6 centistokes at 210.degree. F., 27 to 34 centistokes at 100.degree. F., viscosity indices of 130 to 134, and pour points below -65.degree. F. He contends that the presence of the olefinic products is beneficial in view of the teachings of his earlier patent, U.S. Pat. No. 3,808,134, wherein mixtures of alpha-olefinic oligomers with dialkylbenzenes are claimed to exhibit superior viscosity-temperature properties when compared to either the oligomers or the dialkylbenzenes by themselves. The presence of significant olefinic unsaturation in these oils would, however, be expected to have an adverse effect on the oxidation stability of lubricants formulated therefrom; and, in fact, linear alpha-olefin oligomers are normally hydrogentated to remove residual unsaturation before use -- see, for example, Smith et al U.S. Pat. No. 3,682,823, already cited above.
It must be noted at this point that, by means of the polymerization-alkylation process of U.S. Pat. No. 3,812,036, Romine did obtain three products from n-decene-1 and benzene which contained little or no residual unsaturation. The most viscous of these had a viscosity of 7.79 centistokes at 210.degree. F., 54.02 centistokes at 100.degree. F., a pour point of -65.degree. F., and a viscosity index of 120. These oils are the closest in properties to those of my invention that I am able to locate in the prior art, although my compositions will be seen to be superior thereto and patentable thereover.